Reciprocating piston drive mechanism
A reciprocating piston drive mechanism, especially for a reciprocating piston vacuum pump, includes a cylinder (3) embodied in a housing (12). A piston (4) is moved back and forth in the cylinder by an electromagnetic drive that has an electromagnet (11) on the stator side and at least one permanent magnet (18, 19) on the piston side. In order to increase service life of said drive mechanism, permanent magnets (15, 16) are also provided on the stator side. The piston permanent magnet(s) (18, 19) and the stator permanent magnets (15, 16) are configured and disposed in such a way that the piston (4) is magnetically biased to a substantially central axial position in the idle state.
The present invention relates to a reciprocating piston drive mechanism, especially for a reciprocating piston vacuum pump, comprising a housing, a cylinder embodied in said housing, a piston moving back and forth in the cylinder and an electromagnetic drive for the piston that has an electromagnet on the stator side and at least one permanent magnet on the piston side.
A reciprocating piston drive mechanism having such characteristics is known from DE-A-41 02 710. In this reciprocating piston drive mechanism according to the state-of-the-art there are located in the cylinder two springs, of which one each extends between one of the face sides of the piston and the related face side of the cylinder. Through this, the piston adopts a substantially central axial position in the idle state. When continually stressing the helical springs, fatigue affecting the material of the springs is unavoidable. For this reason, the service life of reciprocating piston drive mechanisms according to the state-of-the-art is thus limited to the service life of the material employed for the springs.
The reciprocating piston drive mechanism according to DE-A-41 02 710 is a component of a reciprocating piston pump, in which at least one of the two chambers created by piston and cylinder has the function of a compression chamber. Located in this chamber or these chambers are the helical springs. This gives rise to unwanted clearance volumes, this impairing the pumping effect.
It is the task of the present invention to improve a reciprocating piston drive mechanism of the aforementioned kind in such a manner that it no longer offers the disadvantage of spring materials being subjected to fatigue. Moreover, the design goal is such that the drive mechanism be particularly well suited for reciprocating piston vacuum pumps.
This task is solved by the present invention in that permanent magnets are provided on the stator side and where the stator magnet(s) is/are so configured and disposed that the piston adopts a substantially central axial position in the idle state. In the idle state, i.e. with the electromagnets de-energised, the superimposed magnetic fields being generated by the permanent magnets affixed to the piston and in the stator, generate forces affecting the piston holding it in a central axial position. Thus in the idle state a defined, for example, central piston position results which is solely effected by the effect of magnetic forces and does not require any additional facility of a mechanical kind, like springs.
It is expedient that the piston be equipped with two permanent magnets, of which one each is located in the area of the two face sides of the piston. Assigned to each of these permanent magnets on the side of the piston is one each permanent magnet on the stator side, specifically in the area of the face sides of the cylinder at an approximately equal radial position.
In a particularly simple solution, the piston is only equipped with a permanent magnet ring arranged approximately centrally in the axial direction. Located to the side of this ring, there is located one each permanent magnet on the stator side, the distances of which with respect to the magnet ring of the piston define the amplitude of the piston's stroke and the desired amount of piston delay as soon as it approaches one of the dead centers.
If the permanent magnets of the stator are magnetised in the axial direction with reversed polarity with respect to the corresponding permanent magnets of the piston, then their magnetic fields will generate repelling forces. These forces then have the effect that the velocity of the piston, as it approaches the face side of the cylinder, is reduced, and finally the movement of the piston in the reverse direction is initiated. If this arrangement is designed to be in all symmetrical, specifically with respect to its dimensions and also with respect to the strength of the magnetic fields, then the piston will, in the de-energised state of the electromagnet's coil, assume a central axial position.
When employing the drive mechanism in accordance with the present invention in a reciprocating piston vacuum pump, an asymmetrical arrangement in the axial direction may be expedient, since the symmetry conditions determine the force characteristic. If the load on the two compression chambers of the pump located at the two face sides is asymmetric during the pumping process, the force characteristic can be adapted by an axially asymmetric drive mechanism.
Further advantages and details of the present invention shall be explained with reference to the schematically depicted design examples of drawing FIGS. 1 to 8.
Depicted are in
drawing
drawing
drawing
drawing
drawing
In the drawing figures in each case the outer housing is designated as 2, the cylinder embodied in the housing 2 as 3, the piston located in cylinder 3 as 4 and its sleeve as 5.
The stator components of the electromagnetic drive mechanism accommodated in the housing in accordance with drawing FIGS. 1 to 5, are at least one coil 8 as well as a pole component 11 (yoke) with a U-shaped cross section open towards the inside encompassing the coil(s) 8 from three sides. Moreover, a pole component 12 (guiding yoke) shaped like a pipe section is provided which is located between coil 8 and sleeve 5. Finally, two permanent magnets 15, 16 which are located in the areas of the face sides of cylinder 3 belong to the stator system. The U-limbs of the yoke 11 terminate at the level of these permanent magnets 15, 16.
Two permanent magnets 18, 19 which are located in the areas of the face sides of the piston 4 are components of the electromagnetic drive mechanism on the side of the piston. In the radial direction, pole components 21 to 24 (drawing
The design of the drive mechanisms depicted in drawing FIGS. 1 to 5 is preferably rotationally symmetrical. Expedient here is the configuration of ring-shaped permanent magnets, both at the stator (15, 16) and also at the piston (18,19). Non-rotationally symmetrical solutions would be more involved as to their manufacture.
In all design examples depicted in drawing FIGS. 1 to 5 in each instance two permanent magnets 18, 19 are provided at the piston substantially at the face side. These might also be replaced by a single piece permanent magnet which, for example, when shaped like a tube encompasses the piston 4.
Expediently reciprocating piston drive mechanisms according to all drawing figures are equipped with sensor components; only in drawing
The reciprocating piston drive mechanisms in accordance with drawing
Drawing
The discharge valves 41, 42 are each arranged on the face side. Preferably the discharge opening substantially extends over the entire cross sectional area of the cylinder 3 (basically known from DE-A-196 34 517). The closure components are designed as flexible discs 43, 44 extending across the entire cross section of cylinder 3, said discs being centrally affixed at housing 2 and being actuated peripherally by the pressure created or by the face sides of the piston. In the example of a design implementation in accordance with drawing
In the implementation in accordance with drawing
Depicted in drawing
In the example of the implementation depicted in drawing
The depicted discharge valves 41, 42 and 41′, 42′ are similarly designed as depicted for the design example in accordance with drawing
Moreover, also different compared to the solution in accordance with drawing
In the example of the design implementation in accordance with drawing
Depicted in drawing
Drawing
In the arrangement in accordance with drawing
There exists the possibility of dispensing with sensor components in the drive mechanism. In this instance the voltage induced in the coil(s) in the stator may be utilised as information for sensing the piston's position, and the subsequent current flow through the same coil(s) may be derived therefrom.
As to the way in which the coil(s) is/are driven, several embodiments are suited for implementation. In the first, an oscillatory frequency is defined at a fixed frequency and the current in the coil(s) is pre-set in such a manner that this frequency is also attained. The motion is reversed at the end position in each case. This approach is termed as “external control”. This principle offers the disadvantage that at very high process loads the pump is prone to being overloaded.
In a second control law, the principle of “self-control” is utilised. In this case the maximum current through the coil(s) is pre-set, and in the event of too high a load the oscillatory frequency is reduced. Here too, the motion is reversed as soon as the piston reaches its end position in each case.
In a third control law, the second control law is varied inasmuch as the motion is reversed already before the piston attains its end position. Thus the reciprocating piston motor can be protected during “pump up” or in the event of continuous and excessively high loads, against being overloaded. In addition, the system may be rated for smaller forces and its implementation can be made to be more cost-effective. The same equally also applies to the second control law.
The example of the implementation of a reciprocating piston vacuum pump in line with the present invention in accordance with drawing
Moreover, from drawing
Claims
1. (canceled)
2. The drive mechanism according to claim 3, wherein:
- the piston is equipped on each of its face sides with the piston permanent magnet; and
- the stator permanent magnets are located in the area of face sides of the cylinder.
3. A reciprocating piston drive mechanism, comprising:
- a housing,
- a cylinder defined in said housing,
- stator permanent magnets disposed in the cylinder,
- a piston mounted for back and forth movement in the cylinder, face sides of the piston being equipped with recesses, which correspond to the dimensions of the stator permanent magnets,
- an electromagnetic drive for the piston including an electromagnet on a stator side and at least one permanent magnet on the piston,
- the stator permanent magnets being disposed relative to the permanent magnet of the piston in such a way that the piston adopts a substantially centered axial position in an idle state.
4. A reciprocating piston drive mechanism comprising:
- a housing,
- a cylinder defined in said housing,
- a piston mounted for back and forth movement in the cylinder,
- an electromagnetic drive for the piston including an electromagnet on a stator side and at least one permanent magnet on the piston,
- stator permanent magnets disposed on the stator side and disposed relative to the permanent magnet of the piston in such a way that the piston adopts a substantially centered axial position in an idle state,
- a pole component with a cross section having a U-shape and U-limbs which end at a level of the permanent magnets on the stator side.
5. The drive mechanism according to claim 4, wherein the U-shaped pole component encompasses at least one coil from three sides.
6. The drive mechanism according to claim 5, wherein a further cylindrical pole component is located between the coil and the cylinder.
7. The drive mechanism according to claim 4, wherein axially arranged pole components are assigned to the permanent magnets at the piston.
8. A reciprocating piston drive mechanism comprising:
- a housing,
- a piston mounted for back and forth movement in a cylinder, the piston being equipped only with a single permanent magnet situated approximately centrally in an axial directions,
- an electromagnet on a stator which interacts with the permanent magnet on the piston to drive the piston,
- stator permanent magnets disposed on the stator and disposed relative to the permanent magnet of the piston in such a way that the piston is biased toward a substantially centered axial position in an idle state.
9. The drive mechanism according to claim 8, wherein permanent magnets on the stator are located on opposite sides of the permanent magnet of the piston, a distance between the permanent magnets on the stator corresponds to an amplitude of the piston's motion.
10. The drive mechanism according to claim 8, wherein:
- two coils are provided next to each other along the axial direction,
- a yoke encompasses the coils,
- a face side of a central yoke component encompasses the permanent magnet of the piston, and
- face sides of inner axially extending yoke components rest against the permanent magnets on the stator.
11. A reciprocating piston drive mechanism comprising:
- a housing,
- a cylinder defined in said housing,
- a piston mounted for back and forth movement in the cylinder,
- a rotationally symmetrical electromagnetic drive for the piston including an electromagnet on a stator and at least one ring-shaped permanent magnet on the piston,
- stator permanent magnets disposed on the stator and disposed relative to the ring-shaped permanent magnet of the piston in such a way that the piston is biased to a preselected axial position in an idle state.
12. The drive mechanism according to claim 11, wherein the stator includes axially symmetrical sole components.
13. A reciprocating piston drive mechanism comprising:
- a housing in which a cylinder is defined,
- a stator surrounding the cylinder,
- a piston mounted for back and forth movement in the cylinder,
- an electromagnetic drive for the piston including an electromagnet, permanent magnets, and pole components in the stator and at least one permanent magnet on the piston, at least one of the pole components interacting with the stator magnets such that resultant magnetic forces are axially asymmetrical,
- the stator permanent magnets being disposed relative to the piston permanent magnet to bias the piston toward a substantially centered axial position in an idle state.
14. A reciprocating piston drive mechanism comprising:
- a housing,
- a cylinder defined in said housing,
- a piston mounted for back and forth movement in the cylinder,
- an electromagnetic drive for the piston including an electromagnet on a stator and at least one permanent magnet on the piston,
- sensors for detecting the piston's position,
- stator permanent magnets disposed on the stator relative to the piston permanent magnet to urge the piston to adopt a substantially centered axial position in an idle state.
15. A reciprocating piston drive mechanism comprising:
- a housing,
- a cylinder defined in said housing,
- a piston mounted in the cylinder for back and forth movement, the piston and the cylinder defining two chambers, at least one of two chambers created by the piston and the cylinder being equipped with an inlet valve and a discharge valve,
- an electromagnetic drive for the piston including a stator electromagnet and at least one piston permanent magnet,
- stator permanent magnets disposed relative to the piston permanent magnet for biasing the piston to a substantially center axial position.
16. A reciprocating piston vacuum pump comprising:
- a housing;
- a cylinder defined in the housing;
- a piston mounted in the cylinder, the piston and cylinder defining a pair of chambers on opposite sides of the piston, the piston mounted for reciprocating movement in the cylinder, which reciprocating movement expands one of the chambers as it contracts the other;
- an inlet line opening into at least one of the chambers, the opening of said inlet line forming together with the piston an inlet valve,
- at least one permanent magnet mounted on the piston;
- permanent magnets mounted on a stator such that magnetic forces between the stator permanent magnets and the piston permanent magnet urge the piston toward a substantially central axial position; and,
- an electromagnet on the stator for selectively urging the permanent magnet on the piston to move the piston along the cylinder.
17. A reciprocating piston pump comprising:
- a housing;
- a cylinder defined in the housing;
- a piston mounted in the cylinder, the piston and cylinder defining a pair of chambers on opposite sides of the piston, the piston mounted for reciprocating movement in the cylinder, which reciprocating movement expands one of the chambers as it contracts the other;
- discharge valves which are controlled by one of pressure and the piston,
- at least one permanent magnet mounted toga piston;
- permanent magnets mounted on a stator such that magnetic forces between the stator permanent magnets and the piston permanent magnet bias the piston toward a substantially centered position axially; and,
- an electromagnet on the stator for selectively urging the permanent magnet on the piston to reciprocate the piston in the cylinder.
18. The sums according to claim 17 wherein the discharge valves include closure pieces which extend substantially over the entire cross section of the cylinder.
19. The pump according to claim 18, wherein closing motion of the closure pieces is assisted by the resilient forces of springs.
20. The sums according to claim 18, wherein closing motion of the closure pieces is assisted by the magnetic forces.
21. The pump according to claim 20, wherein:
- the closure pieces include discs made at least partly of a ferromagnetic material; and
- an outer face side of one of the permanent magnets on the stator forms a discharge valve seat.
22. A reciprocating piston drive mechanism comprising:
- a housing;
- several cylinders accommodated in the housing,
- a piston mounted in each of the cylinders, the pistons and cylinders defining pairs of chambers on opposite sides of each piston, each piston being mounted for reciprocating movement in a corresponding one of the cylinders, which reciprocating movement expands one of the chambers as it contracts the other;
- at least one permanent magnet mounted on each piston;
- permanent magnets mounted on a stator such that magnetic forces between the stator permanent magnets and the piston permanent magnets urge the pistons toward selected axial positions; and,
- an electromagnet on the stator for selectively reciprocating each piston along the corresponding cylinder.
23. A drive mechanism comprising:
- a housing;
- a cylinder defined in the housing;
- a piston mounted in the cylinder, the piston and cylinder defining a pair of chambers on opposite sides of the piston, the piston mounted for reciprocating movement in the cylinder, which reciprocating movement expands one of the chambers as it contracts the other;
- at least one permanent magnet mounted on the piston;
- permanent magnets mounted on a stator such that magnetic forces between the stator permanent magnets and the piston permanent magnet bias the piston;
- an electromagnet on the stator for selectively urging the permanent magnet on the piston to move the piston along the cylinder; and,
- a switching means for driving the electromagnet coil, said switching means being driven by signals dependent on the piston's position.
24. A method for operating a drive mechanism according to claim 13, wherein at least one of a frequency of the piston's motion and a maximum current flow in the electromagnet is pre-set.
25. The method according to claim 24 wherein the piston motion is reversed before reaching an end of travel.
26. A method for operating a drive mechanism according to claim 22, wherein pairs of the pistons are controlled to reciprocate in opposite directions.
27. A piston for a reciprocating piston drive mechanism according to claim 15, the piston including: two pot components which in an area of their open face sides are equipped with joining means.
28. The piston according to claim 27, wherein the pot components are equipped in the area of their open face sides with rims which in the assembled state form a ring groove for accepting a single permanent magnet ring.
Type: Application
Filed: Dec 31, 2003
Publication Date: May 26, 2005
Applicant: LEYBOLD VAKUUM GmbH, a Corporation of Germany (Koln)
Inventors: Rudolf Bahnen (Roetgen), Josef Hodapp (Koln-Sulz), Gunter Knoll (Aachen)
Application Number: 10/749,308